The present invention relates to a footwear having a shell manufactured as one piece by means of injection moulding of polymer material. The present description refers to a downhill skiing boot, but it is understood that the invention also refers to other types of footwear, for example skating boots or working (safety) boots.
As is well-known, in a boot of this kind the shell comprises, as one piece, a rigid sole and two softer sidewalls which extend upwards above the user""s heel. The boot is completed by other structural and functional components, in particular an outer leg-piece hinged on the sidewalls. So as to allow introduction of the foot, the shell is divided, above the sole, by longitudinal (vertical) separation lines into two flaps which overlap over a considerable length in the uppermost part of the boot.
For the dual purpose of facilitating introduction of the foot from above and adapting the internal surface of the shell to the instep of the said foot, the Applicant has for several years now already devised a shell having a slit which is transverse with respect to the longitudinal centre plane and is positioned opposite the user""s heel so as to divide each of the two said flaps into two parts with the mutual possibility of a limited movementxe2x80x94see patent U.S. Pat. No. 4,974,346. In this way each flap of the upper remains attached to the corresponding flap of the leg-piece. In order to minimize the infiltration of snow or water into the boot, without exerting an excessive pressure on the user""s foot, two tongues are used, said tongues being shaped so as to follow the curved form of the shell in the region of the slit The tongues are provided with transverse ribs which are as long as the slit and project as one piece towards the outside. In order to fix on an industrial scale the tongues inside the shell, more precisely either to the two flaps of the upper (i.e. underneath the slit) or to the two flaps of the leg-piece (i.e. above the slit), a heat-welding process is used.
In contrast to the considerable advantages greatly appreciated by the users, of the boots this solution involves for the boot manufacturer not insignificant technical drawbacks relating precisely to the heat-welding process for fixing the tongues:
this process must be carried out on a special production line which is not timed with the other assembly steps of a boot;
there is the risk of small cracks forming in the above mentioned shell flaps, which cracks with repeated use may grow bigger until the boot becomes unusable;
it cannot be used with all types of polymer materials, in particular with polypropylene which would ensure good properties at a relatively low cost.
Cases have also occurred where, owing to poor adhesion of the tongues to the shell flaps following repeated use of the boot, a certain infiltration of snow or water inside the shell occurs, to the obvious disappointment of the user.
It will be desirablexe2x80x94and this in fact forms the main object of the inventionxe2x80x94to provide a reliable boot which may guarantee satisfaction for the users and which does not give rise to the said drawbacks for the manufacturer.